Optical data discs are widely used for digital information storage. In a typical optical storage disc, information is encoded at data-storage positions on the disc in the form of two-state optical "spots" which are read as either "0" or "1". The disc is read by directing a laser beam onto the disc, at selected data-storage positions, and determining from the reflected light beam, which of the two states was seen at each location.
It will be appreciated that the density of stored information in this type of storage disc depends directly on the density of data-storage sites which can be achieved on the disc surface. The site density, in turn, is limited by the ability of the focused laser beam to resolve adjacent data-storage sites. Since a focused laser beam has a spot size of at least about 1-2 microns, the data-storage sites on a disc surface must be spaced by at least 1-2 microns.
It would be desirable to provide an optical data storage disc in which the density of information on the disc can be increased severalfold over current discs.